Telephone system



W. A. MARRISON TELEPHONE SYSTEM Aug. 13, 1940.

4 Sheets-Sheet l Filed-Jan. 21, 1939 5 v at m ul N at at k wt 7 //v VENTOR PKAMARR/SON *MWM A TTORNE V 1940 w. A. MARRISON 2,211,020

TELEPHONE SYSTEM Filed Jan. 21, 1959 4 Sheets-Sheet 2 lNl/ENTOR n. A.MARE/SON BYWWIM A TTORNEV 13, 1940- w. A. MARRISON 2,211,020

TELEPHONE SYSTEM Filed Jan. 21, 1939 4 Sheets-Sheet 3 INVENTORVWAMARRISON Y ATTORNEY w. A. MARRISON 2,211,020

TELEPHONE SYSTEM Aug. 13, 1940.

Filed Jan. 21, 1939 4 Sheets-Sheet 4 INVEN TOR WAMARR/SON ATTORNEYPatented Aug. 13, 1940 UNITED STATES PATENT: OFFICE Y TELEPHONE SYSTEMWarren A. lvlarrison, Maplewood, N. .L, assignor "'to Bell TelephoneLaboratories, Incorporated,

New York, N. Y.,"a corporation'of'lilew York" Application January 21,1939,. Serial No. 252,117.

' 19 Claims. (Cli179 f1 6 This invention relates totelephone systems andparticularly to those in whichautomatic switching equipment is used inthe. establishment of telephone connections.

The objects of the invention. areto obtain greater efficiency andincreased speedxin .the transmission'of telephone designations; tosimplify the operations involved; to reduce the hold:- ing time of theequipment at the central ofiice; and otherwise to secure improvements"and-advantages in systems of this kind. 1 1- Systems have been proposedin the past for transmitting telephone designations, such as the numbersof subscribers? lines or the numbers of trunk circuits, from one pointto another by means of currents ofidiiferent frequencies, the

frequencies singly or'in combination serving to identifythe differentnumerals or other characters of the designation. Where, however,

each character or numeral of a digitaltplace' in the designation isrepresentedby a single frequency it has been necessary to 'transmit insuccession the characters of the successive digital places, since anygiven frequency might be used for two or more places in the samedesignation. Also where the currents-representing,

all of the digital places 'are: sent simultaneously it has beennecessary in these prior systems to utilize combinations of differentfrequency groups for each digital place, the frequencies of a groupserving one digital place differing from those" of the groups servingother places.

The present invention secures advantages over these prior arrangementsin that it is possible to transmit within the same brief. period of timethe characters of all digital places? in a subscribers designation byusing only one frequency for each of the several places, I

According to 'a feature of the invention; this advantage is achieved bya transmission system in which the successive digital places of thedesignation are represented by different frequencies, one for each suchdigital place, and inwhich current of the frequency representing eachplace is transmitted for a brief interval of time, the relative positionof this interval in the total transmission period serving to identify'the'character of the digital place; If,'for example,v a subscribersdesignation has seven digital. or character places, seven differentfrequencies of alternating current are provided, one-for each of theseven digital places" in the designation. The total period oftransmission is then-divided into as many successive intervals as thereare variationsin the character or numeral of. each digital place.Usually, ofcourse,a digital place will have ten different characterscorresponding to the numerals. 1 to 0. .To send the numeral character I,therefore, current of the frequency the period. V. I

In order that the different frequencies representing the differentdigital places and the relativepositionsof the currentintervals duringthe total, transmission period lmay be: identified at the central,ofiice the system is arranged for synchronousoperation of the'substation transmitter and the central office receiving mechanism.

One of the advantages achieved by the present invention, is the abilityof. the calling sub scriber toset up the entire designation on a presettype of transmitter before anyof the des-' ignation currents aretransmitted over the line. Another, advantage is a distinct reductionin-the holding time, of. the common central office equip ment, such, as,the register sender, which receives the transmitted designation andutilizes the same for the purpose of controlling the selective operationof the switches.

. quency during the corresponding intervals of I The foregoing and otherfeatures of this inparts, of a telephone exchange system toillustratethe presentjinvention, g Fig. .1 shows the equipmentv at a subscribersstation, including the designation transmitter;

Fig. 2 illustrates :the automatic switches in the central officetogether with ,a portion of one of the common register senders. Thisfigure also illustrates a called subscribers line; i Figs. 3 and 4disclosejjtheremainder of .thecentral oflice sender partially shown inFig; 2;

Fig. 5 shows an alternative-form of driving mechanism for the substationtransmitter; and Fig.6 shows a detail of the driving'mechanism for thereceiving device at the central office.

The inventionis applicable particularly to systems in which thedigitalzinformation .for a call is registered in a common registersender in the central office, the registered information being utilizedto control the switches in the central office to establish the desiredtelephone connection. To this end the system chosen to illustrate theinvention is one in which the central offices are equipped withautomatic switches of the wellknown panel type. It will be understood,however, that other forms of switches, such as stepby-step switches andcross-bar switches, could be used to establish the connections. In thesystem shown in the drawings many details have been omitted, such as thestructure and circuits of the selective switches, the manner in whichthe sender selectors seize idle senders in response to incoming calls,the manner in which the registers function to control the operation ofthe selector switches, and numerous other details of operation. For abetter understanding of these details reference may be had to manypatents in the prior art relating to systems of this general characterand in particular to the following patents: Stearn et al. No. 1,395,977of November 1, 1921; Stearn No.'1,505,l71 of August 19, 1924; andRaymond et al. No. 1,862,549 of June 14, 1932.

Referring to the drawings, the subscribers line F is equipped at thesubstation with the usual transmission elements, including the talkingtransmitter WI and the receiver I02. The designation transmitter, whichis also provided at the substation in lieu of the usual dial, includes arotary distributor shaft I03 driven by a synchronous motor I 04 to movea plurality of brushes over corresponding rows of fixed segments. Thedesignation transmitter also includes a plurality of manually-operabledevices by means of which the subscriber sets the transmitter inaccordance with the several digital characters of the designation hedesires to transmit. These manuallyoperable devices are illustrated asrotary contact keys I to ill, inclusive, although they may be pushbuttons or levers, or in any other desired form. These digit keys serveto connect corresponding sources of alternating current to the contactsin the corresponding rows of fixed segments in the rotary distributor.

The sources of alternating current are illustrated in the drawings as aseries of generators or oscillators II2 to I I8, inclusive. Each one ofthese generators corresponds to a digital place in a subscribersdesignation and produces a current of a single frequency characteristicof such digital place. For example, generator II2 produces frequency f1which corresponds to and identifies the first digital place in alldesignations that may be transmitted from the substation. Generator .II3 produces frequency f2 corresponding to the second digital place,generator H4 produces frequency f3 corresponding to the third place,and, in like manner, generators H5 to IE8 produce frequencies ]4 to f7,inclusive. The digit key I05 associated with the generator H2 is capableof engaging any one of ten positional contacts which are connectedrespectively to the ten successive segments of the first distributorgroup H9. These ten segments correspond to the ten transmissionintervals which make up the full transmission period. If key I05 engagesthe first contact, connected to the first segment in the group 'I IS,the frequency ii is transmitted during the first interval of the periodand characterizes the digital character I. Similarly if key I05 is inengagement with any one of the successive nine positional contactscorresponding to any one of successive digital places of a designation.

the successive nine segments of the group I I9, the frequency i1 istransmitted during the corresponding interval in the period andidentifies the corresponding numeral 2 to 0. The same is true withrespect to each of the remaining digital keys I06 to III and thecorresponding groups of segments I to I25, inclusive.

As will be explained more fully hereinafter, the synchronous motor I04is set in motion by cmrent supplied from the central office to rotatethe distributor shaft I03 through a single revolution, corresponding tothe total transmission period, during which the brushes of the shaft I03wipe over the corresponding groups of fixed segments to which thegenerators have been connected by the selective positioning of thedigital keys.

The subscribers line I00 appears in the bank of a line finder switch Fat the central ofiice, and the finder F is connected to a first ordistrict selector switch SI. The switch S-I, together with the second orincoming selector S-2 and the final selector S-3, serves to complete theconnection to-a called subscribers line 200 in the event of a localcall. In case the calling subscriber wishes to converse with asubscriber in a distant office the'selector switch S-..I seizes a trunkextending to the distant office where incoming and final selectors arepositioned under the control of the register sender to complete theconnection to .the desired line.

The central office is provided with a plurality of common registersenders, one of which is illustrated in Figs. 2, 3 and 4. These registersenders are selected by means of sender selector switches, oneof which,such as the sender selector S--4, is provided for each link circuitcomprising a line finder F and adistrict selector SI. The senderselector 8-4 is set in motion in response to the act of the. finder F infinding the calling line. Selector S--4 hunts for and seizes the firstidle register sender and associates it with the calling subscribers linethrough the link circuit and the brushes of the line finder F.

- .The register sender in the central ofiice comprises numerous circuitcontrolling relays, a receiving synchronous distributor similar to theone provided at the substation, receiving relays and sets'of registerrelays corresponding to the The rece'ivingdistributor comprises a rotaryshaft 300 operated by a motor L which is driven in synchronism with themotor. IM at the substation, and groups of stationary segmentscorresponding to the successive digital places. For example, the

group of stationary segments 20I corresponds to the first digital placeof the designation and serves to bring about the operation of one of aseries of receiving relays 202 depending upon the value of the digit.Similarly the succeeding groups of segments 203, 204, 205, 205, 20? and208 correspond to the successive digital places and serve to operate therelays of the correspond ing groups of digit receiving relays 209 to 2 I4, re spectively.

The currents of the several frequencies characterizing the digits of acomplete designation are received in the central oflice sender by thecommon receiving circuit 2 I5. After passing through the filter 2I 6,and after being amplified by a suitable amplifier 2, these currents areapplied to I the successive filters 2I8 to 22 3, inclusive. Thesefilters are designed to pass selectively the respective frequenciescorresponding to the generators H2 to H8. Filter 2| 8 passes thefrequency 11 and no other frequencies, filter 2I9 passes frequency f2,filter, 2'20 passes frequency is, and, similarly, filters 22I to 224pass frequencies f4 to f7, respectively.

The currents passing the filters 2I8 to 224 cause the operation ofcertain relays in each of the groups 202 to 2I4, and these relays inturn cause the selective Operation of the corresponding sets of registerrelays shown in Fig. 4. There are seven sets of these registers 400'to406, inclusive, representing in that order the seven successive digitalplaces of a subscribers designation. After the designation has beenregistered on the registers of, Fig. 4, these registers then serve,through the agency of controlling circuits not shown in the drawing, tocontrol the selective operation of the automatic switches S-I,

S2 and 8-3 to extend the calling subscribers line I through to thecalled line 200.v

The operation of the system will now be described in detail, assuming,for this purpose, that the subscriber of line I00 desires to call thesubscriber of line 200 and that the designation of the line 200 is CH3-5000. It will be noted that the first two digital places in thisdesignation are occupied by letters instead of numerals. This practicemakes for ease in remembering the designation, since the letters areusually the first letters of the office name. They are, however, (theequivalent of numerals with regard to the effect they have on thecentral office mechanism.

First the calling subscriber sets up the desired designation on histransmitter. To do this he moves the digital key I to its secondposition contact I26 and the key I06 to the fourth position contact I21,corresponding respectively to the letters C and H of the calleddesignation. He then positions the key I01 on the third contact I26,which corresponds to the character 3 in the ofice code part of thedesignation CH 3. Finally he positions the key I08 on its fifth'positioncontact I29, and the keys I09, H0 and III on their 0 position contactsI30, I3I and I32, corresponding to the numerical portion 5000 of thedesignation. The subscriber then depresses the button I 33, whichlatches and closes the contact springs I34 and I35 to prepare thecircuit for the synchronous motor I04. Finally he removes his receiverI02 from the switchhook, closing the loop of the line I00 and initiatingthe operation of the line finder F at the central office.

When the finder F finds the calling line I00 and the selector S4 extendsthis line through to the idle register sender, a circuit is completedfrom battery to the left winding of relay 225, sender selector brush226, through the contacts of sequence'switch spring 221, thence over thebrush of line finder F over the lower sideof the line I00, through thesubstation circuit and returning over the upper side of the line throughthe brush of finder F, contacts of sequence switch spring 228, brush 229thence to ground in the register sender. The relay 225 operates andcloses a circuit from battery through thewinding of relay 230, contactof relay 225 to ground at the left back contact of relay 23I. Relay 230operates and connects the source of alternating current 232 to thesynchronous motor 30I associated with the receiving distributor of thesender and simultaneously to the synchronous motor I04 associated withthe transmitter at the subscribers station. The circuit for motor 30Imay be traced from the generator 232, through the outer contacts ofrelay 230, right contacts of relay 23I and thenceover .thecircuit 233 tothe motor 30I. The circuit for motor I 04.: at the substation may betraced from generator 232 through the inner ,contactsof relay 230through filter 234 thence over circuit 2I5 through the brushes 226 and229 and thence over the subscribers line I00 through the filter I36 tothe windings of the motor I04.

The-filters I36 and 234 pass current of the frequency produced by thegenerator 232 and exclude currents of other frequencies. Similarly thefilter 2I 6 prevents current from source 232 from passing to the commonreceiving circuit When relay 225 operates, it also closes an obviouscircuit for relay 244. Relay 244 closes a circuit from battery throughthe windings of all of the relays 401, 4, M2, M3, M4, M5 and M6 inparallel, thence over common conductor 4I1, outer contacts of relay 244,thence over conductor 245 to ground over the contacts of each of therelays M0, M8, M9, 420, 42I, 422 and 423. The relays 401, 4, M2, M3, M4,M5 and M6 serve respectively to connect the successive registers 400 to406 through to the contacts of the digit receiving relays 202, 209,2I0,- 2II, 2I2, 2I3 and2l4.

The distributor shafts I03 and 300 rotate in synchronism with each otherthrough a complete cycle, which corresponds to the transmission period.Since these shafts are in synchronism with each other, their brushesengage simultaneously the segments corresponding to the ten successivepositions 1 to 0. When theshaft 300 'moves out of its normal position, acircuit is closed from battery through the winding of relay 262, segment263 and thence through the When the shafts I03 and 300 reach the sec-0nd position segments, the first impulse is sent for the assumeddesignation. The circuit for this purpose is closed from the right poleof generator I I2 through the key I05, contact I26, segment I31 of thegroup II9, distributor shaft I03, common segment I38, conductor I39,thence over the lower conductor of line I00 through the finder F, spring221, brush 226, conductor 235 to the filter 2I6. The other side-of thecircuit may be traced from the other pole of the filter 2I6, back overconductor 236 through the brush 229, spring 228 through the finderswitch F, thence over the upper side of the line through conductor I40and finally to the left pole of the generator II2. Current of thefrequency ii is transmitted to the, central oifice, where it passes thefilter 2I6 and is amplified by the amplifier 2" and delivered to thecircuit 231, which is common to all of the filters 2 I8 to 224,inclusive. Since the current thus transmitted is of the frequency f1, itis passed selectively byv the filter 2I8 and current is caused to flowin the output circuit of the filter, which may be traced by way ofconductor 238 through the winding of the receiving relay 239 of, thegroup 202, thence to the second position segment 240, with which thebrush shaft 300 is now in engagement, over said brush shaft through thecommon segment 24I, conductor 242 to the other terminal of the outputcircuit of filter 2I8. Relay 239 operates in this circuit and closes acircuit from ground through its. contact, conductor .243 through the.closed lcontact'of relay 401, left winding of register relay 458 tobattery. Relay 458 operates and locks in acircuit from battery throughits right winding and contact, conductor 409 through the winding ofrelay 4Ifl to ground. Relay 4 Ill operates in series with the registerrelay and removes its ground connection from the common conductor 245.Relay 491, however, remains operated as long as ground is present on thecommon conductor 245.

When the distributors reach their third position contacts, a circuit isclosed from the right terminal of generator II4, digit key I01, terminalI28, segment I4l, shaft I03 common segment I38 thence over the linecircuit to the filter 2IB and returning over the line by way ofconductor I40 to the other pole of generator II 4. A current offrequency is is transmitted over this circuit and thence to the commoncircuit 231. Since the filter 220 is tuned to frequency f3, currentflows in the output circuit of filter 226 over conductor 245 through arelay in the group 259 corresponding to relay 247, over conductor 248,segment 249, shaft 380, common segment 24I, conductor 242 to the otherterminal of the filter 220. The operated relay of the group 2I0 appliesground potential to conductors 25B and 25I, which extend through thecontacts of relay M2 to the windings of register relays 424 and 425.Relays 424 and 425 operate and look through their right windings andcontacts over conductor 432 to the winding of relay M9 to ground,operating relay 4I9.

When the distributors reach their fourth position'contacts the generatorH3 at the substation is connected by way of digit key I06 and segmentI42 to the line, and a current of frequency f2 is transmitted. Currentof this frequency passes the selective filter 2I9 and operates thefourth receiving relay of the group 209 by way of a circuit includingconductor 252, conductor 253 and segment 254. The operated relay of thegroup 2553 applies ground potential to conductor 255 which extendsthrough a closed contact of relay 4II to the left winding of registerrelay 425. Register relay 426 operates and locks through its rightwinding and the winding of relay 4I8. Relay 4l8 also operates andremoves its ground connection from the common conductor 245.

When the synchronous distributors reach their fifth position segments,the generator IE5 is connected to the line by way of digit key I68 andsegment I43. Current of the frequency f4 flows over the line and ispassed by the filter 22! in the sender. Current flowing in the outputcircuit of the filter 22I causes the operation of the fifth relay of thegroup 2I I by way ofa circuit including conductor 256, conductor 25! andthe fifth segment 205 of the distributor. The operated relay of thegroup 2 applies ground potential to conductor 258, which extends throughthe operated contacts of relay M3 to the left winding of register relay427. Relay 421 operates and locks in series with relay 420, the latterrelay also operating.

Since the numeral occurs in each of the last three places of thedesignation, no more currents are transmitted until the synchronousdistributors reach their last or 0 position segments. On reaching thelast segments in the distributor groups, circuits are closed forconnecting the three generators IIG, Ill and H8 simultaneously to theline. The generator H6 is connected by Way of digital key I09 anddistributor segment I44, generator II! is connected by way. of key Ill]and distributor segments I45, and generator I I8 is connected by way ofkey I I I and distributor segment I46. i Currents of frequencies f5, f5,and J? are transmitted over the line and are selected respectively byfilters 222, 223and 224. In the manner already described I currentsflowing in the output circuits of these filters cause the operation ofthe tenth relay in the relay groups 2I2, 2I3 and 2I4. These relays applyground potential to conductors 259, 260 and 25!, which extendrespectively through the contacts of relays 4 I 4, 4| and 4 I 5 to thewindings ofrelays 428, 429 and 430. These register relays operate andlock, respectively, through the windings of relays 42!, 422 and 423.Relays 42I, 422 and 423 operate, and, since all of these relays are nowenergized, ground potential is removed from the common conductor 245 topermit the release of 1'elays4fil', 4H, 4I2, M3, M4, M5 and M5. Theserelays disconnect the receiving relays shown in Figs. 2 and 3 from theregister relays shown in Fig. 4.

The entire designation has now been transmitted to the central ofliceand registered on the register relays in the sender. It will be notedthat the order in which the short current impulses are transmitted overthe line does not bear any definite relation to the sequence of thedigital places in the designation. Instead the order of transmitting theimpulses representing the different digital places depends upon thevalue of the digit. These current impulses may be transmitted insuccession if the digit values occur in that manner or two or more ofthem may be transmitted simultaneously, as in the case of the last threedigits in the assumed designation. Or the impulses in some cases may besent in the inverse order of the sequence of digital places.

As the distributor shaft I03 at the substation approaches its normalposition the uppermost end thereof engages the dog I41, causing it totilt and release the switch springs I34 and I35. This opens the circuitof the motor I54, bringing the distributor to rest in its normalposition. Also as the distributor shaft 300 of the distributor at thecentral office approaches its normal position, a circuit is closed forthe relay 23I extending from battery through the winding of said relay,closed contacts of relay 2B2, segment 26! thence through brushes of thedistributor to the grounded segment 264. Relay 23I opens its rightcontacts and also releases relay 236. Thus the source of current 232 isdisconnected from the subscribers line and also from the synchronousmotor 3M and the distributor shaft 309 comes to rest in its normalposition.

The register sender now proceeds to control the selective operation ofthe switches SI, S2 and S-3 in accordance with the designationregistered on the register relays of Fig. 4 to extend the callingsubscribers line Hill through to the called line 2053. Thereafter theregister sender restores to normal and is ready for use in connectionwith another call.,

If it is desired to dispense with the synchronous motor for operatingthe distributor at the substation, this may be accomplished by providinga driving mechanism the power for which is stored up by an act of thesubscriber and which is controlled by a governing device to operate thedistributor at a speed which corresponds substantially to the speed ofthe distributor in the central office sender. A driving mechanism forthe substation distributor is illustrated in Fig. 5. To set the devicefor operation the subscriber seizes the knob I48 and pulls the bar I49outwardly against the tension of the spring I50. The rack on the bar I49rotates the shaft I5I through an angle corresponding to a rotation ofthe distributor shaft I03. The subscriber then releases the bar I49, andthe spring I50, being under tension, tends to drive the shaft I52through the pawl I 54 and ratchet I55. However, shaft I52, to which theratchet I55 is attached, is held in its position by the latch magnetI53". When the system is ready for the transmission of impulses, currentflowing from the central ofiice over the line causes the operation ofthe latch magnet I53, which attracts its armature and releases thedriving mechanism. The spring I50 thereupon rotates the shaft I5 I, and,through the pawl and ratchet connection, the shaft I52, which in turndrives the distributor shaft. The speed of the distributor shaft isclosely regulated by a governor device I56. At the same time thedistributor in the central office sender is set in rotation and operatesin synchronism with the distributor at the substation.

An alternative form of driving mechanism for the distributor at thecentral office is illustrated in Fig, 6. Here the synchronous motor I51is connected through a friction clutch I58 to the shaft I59 which drivesthe distributor. To rerelease the distributor for operation followingthe application of current to the motor I51, an impulseis transmitted tooperate the trip magnet I60. The magnet I60withdraws the latch andallows the motor I51 to drive the shaft I59 through the friction clutchI58.

What is claimed is:

1. In a telephone system, a telephone line having a subscribers stationthereon, means for producing currents of a plurality'of differentfrequencies, each frequency representing a different digital place in atelephone designation, a transmitting device at said station having aperiod of operation comprising a plurality of successive intervals oftime, said transmitting device including means for applying to said linecurrent of each of said frequencies for a time equal to one of saidintervals, and means for selecting any one of the successive intervalsof said period for application to designate the value of the characterin the digital place represented by the frequency applied.

2. In a telephone system, a telephone line having a substation thereon,means for producing alternating currents of a plurality of differentfrequencies, a single frequency serving to identify a particular one ofthe several digital places in a telephone designation, a transmittingdevice at the substation having a definite cycle of operation which isdivided into a plurality of short successive intervals of time, saidtransmitting device including means for applying to the-line each one ofsaid frequency currents for a time equal to one of said intervals withina single cycle" of operation of said transmitting device, and manuallyoperable means under control of the subscriber at the substation forvarying in said cycle the relative position of the interval ofapplication of each of said frequency currents to designate the value ofthe digital character in each of the digital places of the designation.

3. In a telephone system, a telephone line having a subscribers stationthereon, means for producing currents of a plurality of differentfrequencies, each frequency representing a different digital place in atelephone designation, a transmitting device at said station having aperiod of operation comprising a plurality of successive intervals of.time, said transmitting device includingr'neans for applying to said,line current of each of said frequencies for a time equal to one ofsaid intervals, means capable of being positioned inadvance by thesubscriber for selectingany one of the successive intervals in saidperiod for the application of each of said frequency currents todesignate the value of the characters in each of the digital places, andmeans for operating said transmitting device, after the selections forall digital places have been made.

4.- In a telephone system, a telephone line having a subscribers stationthereon, means for producing currents of a plurality of differentfrequencies, each frequency representing a different digital place in atelephone designation, a transmitting device at said station having aperiod of operation comprising a plurality of successive intervals oftime corresponding to the different characters in a digital place, aplurality. of. digit keys capable of being preset by the subscriber inaccordance with a wanted designation, each key representing a differentfrequency and serving toselect any one of said successive intervals, andmeans for operating said transmitting device to send over the linecurrent of all of said frequencies during the particular intervalsofsaid period determined by the settings of the corsponding'digitalplace, means at the central ofiicefor selecting said impulses inaccordancewith' their frequencies, and means for utilizing the selectedimpulses to control the operation of said automatic switches. I Y

6. In a telephone system, a central office, a subscribers line,automatic switches in the central office for extending said line, atransmitting device at the substation of said line having a period ofoperation, means for operating said device to send over the line aplurality of current impulses of different frequencies, each frequencyserving to identifya digital place in a telephone designation, means forvarying the chronological position of each impulse in said period toidentify the character in the corresponding digital place, 'registersatthe central office for controlling-said automatic switches, saidregisters corresponding respectively to the digitalplaces of thedesignation, means for selecting each impulse transmitted in accordancewith its frequency, and

means operable in accordance with the chrono' logical position of eachselected impulse for setting the corresponding register.

tral office for extending said line, a transmitting device at thesubstation of said line having a" period of operation, means for drivingsaid device through its period of operation to send over the line aplurality of current impulses of different frequencies, each frequencycorresponding to a digital place in a telephone designation, means forvarying the chronological position of each im- 65 7. In a' telephonesystem, a central office, a subscribers line,automatic switches in thecenpulse in said period to determine the value of the digit in thecorresponding digital place, means at the central office for selectingsaid impulses according to their frequencies, registers for controllingsaid automatic switches, and means operating in synchronism with thetransmitting device for determining the chronological position of theselected impulses and for causing the operation of said registers toregister the transmitted designation.

8. The method of transmitting designations in a telephone exchangesystem which comprises applying to a telephone line during the period oftransmission a pattern of current impulses in which the digital placesof a designation are distinguished from each other by differences in thefrequencies of said impulses and the char acters of the digital placesare identified by the chronological positions of the current impulses insaid transmission period.

9'. The method of transmitting designations in a telephone system whichcomprises applying to a telephone line during a definite period oftransmission a pattern of current impulses in which each digital placeof a telephone designation is identified by a single impulse of adistinctive frequency and the characters of each digital place areidentified by the relative position of the impulse in said transmissionperiod.

10. The method of transmitting a digit of a multidigit telephonedesignation which comprises applying to a telephone line an impulse ofalterhating current which identifies the character of the digit by thechronological position of the time interval in which the impulse occursduring the transmission period and distinguishes its dig-- ital placefrom other digital places in the designation by the frequency of theimpulse.

11. The method of transmitting a multidigit telephone designation in agiven time period, in which the several digital places are representedrespectively by brief intervals of current of distinguishing frequenciesapplied to a telephone line, and in which the character value of eachdigital place is determined by the position in the transmission periodof the brief interval of current representing such digital place.

12. The method of transmitting, within a period of time consisting of aplurality of successive r i brief intervals, 2. multidigit telephonedesignation which comprises identifying each of the digital places ofthe designation by transmitting a single impulse of current ofdistinguishing frequency over a telephone line during any one of saidbrief intervals, and identifying the characters of the digit of eachplace by transmitting the impulse of distinguishing frequency during thecorresponding one of said intervals.

13. The method of transmitting designations in a communication system,in which a designation comprises a series of units, in which the severalunits are represented respectively by brief intervals of current ofdistinguishing frequencies applied within a given period of time to atransmission circuit, and in which the character of each unit isidentified by the chronological position of the current interval in saidperiod.

14. The method of transmitting in a given period of time a signalcomprising a series of units, in which each of the signal units isrepresented by an interval of current of a distinguishing frequency, andin which the character of the signal unit is identified by thechronological position of the interval of current in the transmissionperiod.

15. The method of transmitting information in a communication systemwhich comprises applying to a transmission circuit within a given periodof time a current pattern in which different portions of the informationare represented by intervals of current of distinguishing frequencies,and in which the character of each portion of the information isidentified by the chronological position of the current interval in saidperiod of time.

16. In a telephone system, a telephone line having a subscribers stationthereon, means for producing currents of a plurality of differentcharacteristics, each characteristic representing a different digitalplace in a telephone designation, a transmitting device at said stationhaving a period of operation comprising a plurality of successiveintervals of time, said transmitting device including means for applyingto said line current of each of said characteristics for a time equal toone of said intervals, and means for selecting any one of the successiveintervals of said period for application to designate the value of thecharacter in the digital place represented by the characteristic currentapplied,

1'? In a telephone system, a telephone line having a subscribers stationthereon, means for producing currents of a plurality of differentcharacteristics, each characteristic representing a different digitalplace in a telephone designation, a transmitting device at said stationhaving a period of operation comprising a plurality of successiveintervals of time corresponding to the different characters in a digitalplace, a plurality of digit keys capable of being preset by thesubscriber in accordance with a wanted designation, each keyrepresenting a different characteristic current and serving to selectany one of said successive intervals, and means for oper ating saidtransmitting device to send over the line currents of all of saidcharacteristics during the particular intervals of said perioddetermined by the settings of the corresponding keys.

18. The method of transmitting designations in a telephone exchangesystem which comprises applying to a telephone line during the period oftransmission a pattern of current impulses in which the digital placesof a designation are distinguished from each other by differences in thecharacteristics of said impulses and the characters of the digitalplaces are identified by the chronological positions of the currentimpulses in said transmission period.

19. The method of transmitting a multidigit telephone designation in agiven time period, in which the several digital places are representedrespectively by brief intervals of current of distinguishingcharacteristics applied to a telephone line, and in which the charactervalue of each digital place is determined by the position in thetransmission period of the brief interval of current representing suchdigital place.

WARREN A. MARRISON.

